Difference between Inverting and Non-Inverting Amplifier


In electronic circuits, we use an electronic device called operational amplifier (Op-Amp). The operational amplifier is a high-gain multistage differential amplifier. It has two inputs and one output, where the input terminals are named as inverting terminal and non-inverting terminal. The inverting terminal of the Op-Amp is marked with positive (+) polarity, whereas the noninverting represents the negative (-) polarity terminal.

Depending on the circuit configuration, the operational amplifier is classified into two types namely,

  • Inverting Amplifier
  • Non-Inverting Amplifier

This article is meant for explaining the differences between an inverting amplifier and a noninverting amplifier. But before that, let's understand the basics of inverting amplifier and noninverting amplifier so that it becomes easy to the differences between them.

What is an Inverting Amplifier?

An operational amplifier (or Op-Amp) which is designed to produce an output signal that is 180° out of phase with the applied input signal is called an inverting amplifier.

Therefore, in case of an inverting amplifier, if the input signal has positive phase then the amplified output signal will have negative phase and vice-versa. The inverting operational amplifier is the simplest and most extensively used configuration of the operational amplifiers.

Figure-1 shows the typical circuit of an inverting amplifier. From this circuit, it is clear that a feedback signal is provided in the operational amplifier so that the circuit can perform the closed loop operation. It may also be noted that the feedback provided is the negative one, which increases the accuracy of operation of the circuit.

The closed loop gain of the inverting amplifier (shown in Figure-1) is given by the following expression −

$$A_v\:=\:\frac{V_{out}}{V_{in}}\:=\:-\frac{R_2}{R_1}$$

Where, R2 is the feedback resistance and R1 is the resistance between source and input terminal.

Inverting amplifiers are used in a number of applications like phase shifter, integration, signal balancing, mixer circuits, etc.

What is a Non-Inverting Amplifier?

A type of operational amplifier in which the input signal and the amplified output signal have the similar phase, then the amplifier is known as non-inverting amplifier. Thus, in case of a non-inverting amplifier, if the input signal has a positive phase, then the amplified output signal will also have the positive phase and the same is true for negative phase.

The typical circuit configuration of a non-inverting amplifier is shown in Figure-2. In this amplifier, the input signal is applied at the non-inverting terminal, while the feedback is provided at the inverting terminal. Thus, the non-inverting amplifier has a negative feedback.

The following expression gives the closed loop gain of the non-inverting amplifier,

$$A_v\:=\:\frac{V_{out}}{V_{in}}\:=\:1+\frac{R_2}{R_1}$$

Non-inverting amplifiers are used in circuits where high input impedance is required. They are used as a voltage follower, isolation of cascaded circuits, to perform mathematical simulations, etc.

Difference between Inverting Amplifier and Non-Inverting Amplifier

The following table shows the major differences between an inverting amplifier and a non-inverting amplifier −

Basis of Difference Inverting Amplifier Non-Inverting Amplifier
Definition A type of operational amplifier which generates an amplified output signal that is 180° out of phase with the input signal is called an inverting amplifier. A type of operational amplifier which generates an amplified output signal that is in phase with the applied input signal is called a non-inverting operational amplifier.
Input In case of an inverting amplifier, the input signal is applied at the negative (called inverting) terminal of the amplifier. In a non-inverting amplifier, the input signal is applied at the positive (called non-inverting) terminal.
Phase difference between input & output signals In the inverting amplifier, there is a phase difference of 180° between the input signal and output signal. Hence, the input and output signals are out of phase in case of an inverting amplifier. The non-inverting amplifier has a phase difference of 0° between the input and output signals. Therefore, the input and output signals are in-phase with each other in case of a noninverting amplifier.
Feedback In the inverting amplifier, the feedback is provided at the same terminal at which the input signal is applied. In the non-inverting amplifier, the feedback signal (negative terminal) and input signal (positive terminal) are connected to different terminals.
Ground terminal The positive terminal of the inverting amplifier is connected to the ground. The negative terminal of the noninverting amplifier is connected to the ground.
Feedback ground In the inverting amplifier, the feedback is not connected to ground. In the non-inverting amplifier, the feedback is connected to ground through a resistance (in our case R1).
Nature of output The inverting amplifier produces an inverted output which is expressed with negative polarity. The output produced by a noninverting amplifier is non-inverted in nature and expressed with positive polarity.
Expression of closed loop gain The closed loop gain of an inverting amplifier is $$A_v\:=\:-\frac{R_2}{R_1}$$

Thus, the gain of the inverting amplifier is just a ratio of resistances.

The closed loop gain of a non-inverting amplifier is $$A_v\:=\:1+\frac{R_2}{R_1}$$

Hence, the gain of the non-inverting amplifier is the sum of 1 and the ratio of resistances.

Gain polarity The polarity of gain of an inverting amplifier is negative. The polarity of gain of a non-inverting amplifier is positive.
Gain value The gain of an inverting amplifier may be less than, more than or equal to unity (1). The gain of a non-inverting amplifier is always more than 1.
Input impedance The input impedance of an inverting amplifier is equal to R1 (refer Figure-1). The input impedance of a noninverting amplifier is extremely high.
Applications The applications of inverting amplifiers are: in trans-resistance amplifiers, at the output stage in the circuits designed with different types of sensors, integrator circuits, phase shifter, etc. The applications of the non-inverting amplifiers are: in the circuits that require high input impedance, isolation of cascaded circuits, changing gain considerations, voltage followers, etc.

Conclusion

The most significant difference is that an inverting amplifier introduces a phase shift of 180° between the input and output signals, whereas a non-inverting amplifier has 0° phase shift (nophase shift) between input and output signals. Both inverting and non-inverting amplifiers use negative feedback which increases the controllability of the gain of the amplifier.

Updated on: 02-Nov-2023

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